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<head>
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<meta name="viewport" content="width=device-width,user-scalable=no" />
<title>Document</title>
<style type="text/css">
#box {
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	height: 100px;
	border: 1px solid #000;
	margin: 30px auto;
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	perspective: 300px;
} 
#div {
	width: 100px;
	height: 100px;
	background: red;
	-webkit-transform: rotateY(30deg);
	transform: rotateY(30deg);
}
</style>
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window.onload = function(){
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	console.log(getComputedStyle(div)["transform"]);
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<div id="box">
	<div id="div"></div>
</div>	
</body>
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